The present invention is related to a converter outputting appropriate screen resolutions according to different aspect ratios, and more particularly for a digital television system.
In the United States, the digital television (TV) standard allows many types of video image formats, with different screen resolutions of 480.times.640, 480.times.704, 720.times.1280, 1080.times.1920. Thus, a digital TV system must be capable of processing a variety of image sizes, especially because image formats may constantly change, even for the same channel. Additionally, each image size may have different aspect ratios of either 4:3 or 16:9. If the input aspect ratio is 4:3 and the display screen aspect ratio is 16:9, the image may be shown in either 4:3 or 16:9 aspect ratios.
FIG. 1 shows a system for converting the 4:3 input aspect ratio to a 16:9 display aspect ratio. Such system includes a format detector 10, a converters 12 consisting of a 640:854 converter 120, a 704:854 converter 122, a 720:854 converter 124, a 768:854 converter 126, and a multiplexer (MUX) 14. In operation, the format detector 10 receives input image with 4:3 aspect ratio and detects the image size. According to the detected size, the format detector 10 generates an output signal selecting the appropriate converter. The MUX 14 receives the output signal of the format detector 10 and output an image with 16:9 aspect ratio through converters 120, 122, 124, 126.
Generally, an image with 4:3 aspect ratio has 480 scanning lines with any one of the image sizes from 480.times.640, 480.times.704, 480.times.720 and 480.times.768. However, an image with a 6:9 aspect ratio has an image size of 480.times.854. Thus, depending on the input image size, one of converters 120, 122, 124, or 126 will be used to convert an image with a 4:3 aspect ratio to an image with 16:9 aspect ratio.
According to the past aspect ratio converting systems for a digital TV, different converters were used to convert each different image size. However, converters are difficult to manufacture and more importantly, it is difficult to output an image size of exactly 480.times.854 for 16:9 aspect ratio.